Hydroxycarboxylic acids (HCA's) are an especially interesting and useful class of compounds. They are, by their very nature, bifunctional and therefore allow for a multitude of chemical transformations. Both functional groups, i.e., the hydroxy and the carboxylic acid groups, can, under certain conditions, react independently of one another, thereby generating the classical derivatives of each group, yet at other times may interact with each other to perturb their normal chemical reactivities. Also of interest is the possibility for reaction between the two functional groups leading to dimeric, oligomeric, and, importantly, polymeric materials. In the case of beta-hydroxycarboxylic acids (β-HCA's), there is also the possibility of dehydration via loss of the hydroxy group and an adjacent hydrogen atom. Such dehydration can lead to the formation of alpha, beta-unsaturated carboxylic acids, an important class of compounds in their own right.
Two very common and commercially important alpha, beta-unsaturated carboxylic acids are the acrylate and methacrylate families. Acrylic acid, salts of acrylic acid, and esters of acrylic acid are used in the manufacture of polyacrylic acid, polyacrylic acid salts, and polyacrylates. These materials are useful as surface coatings, adhesives and sealants, absorbents, textile and non-wovens, and plastic modifiers.